This invention relates to an overtemperature and overcurrent resistor fuse.
A conventional overtemperature and overcurrent resistor fuse comprises a resistor body having finely divided conducting powder, silica powder and an additive powder dispersed in resin, said additive powder having a transforming temperature in the range from Tg.degree.C to (Tg.degree.C+200.degree.C), wherein Tg.degree.C is the glass transition temperature of said resin. Such a resistor fuse is disclosed in U.S. Pat. No. 3,745,507. Such a resistor fuse, however, has the disadvantage that when it is operated under an overload condition such as a wattage of from 5 to 50 times the rated wattage, the resistor or fuse has a slow irreversible increase of electrical resistance. Moreover, when a current which produces a wattage larger than a wattage 50 times the rated wattage flows through the resistor fuse, it is rapidly heated by well known Joule-heating. Because of the heat, the resistance of the resistor fuse decreases. Because of this decrease of resistance, the current flowing through the resistor fuse increases, and so the resistor fuse is heated even more by Joule-heating. Due to this vicious circle, the resistor fuse is finally short-circuited, arcing occurs, or the resistor fuse burns or becomes charred or softened. Accordingly, there has been difficulty in providing a resistor fuse which is free from above mentioned disadvantage for a relatively low electrical resistance below 1.OMEGA., even if the resistor fuse is operated under serious overload or overheating conditions.